Electric motor with harmonic shunting

ABSTRACT

Disclosed is a hermetic AC electric motor that includes harmonics shunting such that high frequency harmonics are shunted from the AC electric motor without the use of one or more high frequency filters in the associated motor drive. A related method of operating an AC electric motor includes shunting high frequency harmonics to a fluid passing through the AC electric motor. Also disclosed is a simplified variable speed motor drive system which eliminates the need for a filter for removing high frequency harmonics.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of and priority to U.S. ProvisionalApplication Ser. No. 62/355,698 entitled “ELECTRIC MOTOR WITH HARMONICSHUNTING” and filed Jun. 28, 2016, the entirety of which is herebyincorporated by reference herein for all purposes.

BACKGROUND 1. Technical Field

The present disclosure is directed to systems, apparatus, and methodsfor thermal management of electrical machines (e.g., compressor motorsin chillers), and in particular, an improved variable speed electricmotor and drive system that eliminates the need for drive currentharmonic filters.

2. Background of Related Art

In AC electric motors, motor temperature rise results from thecirculation of high frequency currents which do not contribute tomagnetic flux production in the air gap, but rather dissipate in themotor stator and/or rotor as Joule loss. Existing methods to mitigatethis issue include installation of passive filters (e.g., L, LC, etc.)between the motor and drive, use of multi-level inverters, pulse widthmodulation (PWM) optimization patterns and increasing switchingfrequencies. Each of these methods is costly, bulky, and can result onoverall system derating (e.g., insulated gate bipolar transistor (IGBT)and associated power module de-rating at higher switching frequencies).Cost, loss, and rating of high speed motors and drive systems aresignificantly impacted by high frequency harmonics.

SUMMARY

A hermetic AC electric motor includes harmonics shunting such that highfrequency harmonics can be shunted from the AC electric motor withoutthe use of one or more filters. The motor can further include a statorand a rotor disposed within the stator and in selective magneticcommunication with the stator. A fluid gap can exist between the rotorand the stator. The fluid gap can be configured to receive a coolingfluid. A cage can be disposed on the rotor configured to receive highfrequency harmonics and shunt the high frequency harmonics to thecooling fluid.

The rotor can include surface permanent magnets and the cage includes aplurality of aluminum wedges, each wedge disposed between each surfacepermanent magnet. In certain embodiments, the cage can include one ormore aluminum spacers disposed around the rotor. The one or morealuminum spacers can include a thick spacer and two thin spacersdisposed axially away from the thick spacer on opposite sides of thethick spacer. The motor can further include a carbon fiber sleevedisposed around the rotor and the cage.

The motor can include a stator, and a rotor that includes a shaft, aneddy current shield disposed around the shaft, and a plurality ofmagnets disposed around the eddy current shield. The eddy current shieldis configured to receive high frequency harmonics and to shunt the highfrequency harmonics to the shaft, and to the cooling fluid. A sleeve,which can be made of carbon fiber, may be disposed around the rotor. Theeddy current shield can be formed from copper.

In accordance with at least one aspect of the present disclosure, asystem includes an AC electric source that outputs high frequencyharmonics, and a hermetic AC electric motor connected to the AC electricsource without one or more filters. The AC electric motor includesharmonics shunting such that the high frequency harmonics are shuntedfrom the AC electric motor without the use of one or more filters.

The hermetic AC electric motor of the system can further include astator and a rotor disposed within the stator and in selective magneticcommunication with the stator. A fluid gap can exist between the rotorand the stator. The fluid gap can be configured to receive a coolingfluid. A cage can be disposed on the rotor configured to receive highfrequency harmonics and shunt the high frequency harmonics to thecooling fluid.

The rotor can include a plurality of surface permanent magnets and thecage can include a plurality of aluminum wedges. Each wedge is disposedbetween two surface permanent magnets. In certain embodiments, the cagecan include one or more aluminum spacers disposed around the rotor. Theone or more aluminum spacers can include a thick spacer and two thinspacers disposed axially away from the thick spacer on opposite sides ofthe thick spacer. The motor can further include a carbon fiber sleevedisposed around the rotor and the cage.

The hermetic AC electric motor of the system can include a stator, and arotor that includes a shaft, an eddy current shield disposed around theshaft, and a plurality of magnets disposed around the eddy currentshield. The eddy current shield is configured to receive high frequencyharmonics and to shunt the high frequency harmonics to the shaft, and tothe cooling fluid. A sleeve, which can be made of carbon fiber, may bedisposed around the rotor. The eddy current shield can be formed fromcopper. The cage may be formed from aluminum.

The system can include a chiller compressor connected to the AC electricmotor. The fluid gap of the AC electric motor can be in fluidcommunication with a refrigerant of the chiller to cool the AC electricmotor to thermally shunt the high frequency harmonics.

In accordance with at least one aspect of this disclosure, a methodincludes shunting high frequency harmonics to a fluid passing through ahermetic AC electric motor. The method can include providing ACelectrical energy from an AC electric source directly to the AC electricmotor without passing the AC electric energy through a filter. The ACelectric energy can include the high frequency harmonics.

Shunting can include thermally shunting the high frequency harmonics byconverting the high frequency harmonics to thermal energy in a structurethat is configured to be in thermal communication with the fluid passingthrough the AC electric motor. In certain embodiments, the structurethat is configured to be in thermal communication with the fluid passingthrough can be a cage on a rotor of the AC electric motor.

In some embodiments, the structure that is configured to be in thermalcommunication with the fluid passing through the AC electric motor is ashaft of a rotor of the AC electric motor. In some embodiments, theshunting includes converting the high frequency harmonics to thermalenergy in an eddy current shield disposed between a shaft and a magnetof a rotor of the AC electric motor.

In accordance with at least one aspect of this disclosure, a hermetic ACelectric motor system does not include a filter for removing highfrequency harmonics.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the disclosed system and method are describedherein with reference to the drawings wherein:

FIG. 1 is a cross-sectional view of an embodiment of a hermetic ACelectric motor in accordance with the present disclosure;

FIG. 2A is a perspective view of an embodiment of a rotor in accordancewith the present disclosure;

FIG. 2B is a perspective view of the rotor of FIG. 2A, shown with asleeve disposed thereon;

FIG. 2C is a cross-sectional view of the rotor of FIG. 2A;

FIG. 2D is a longitudinal cross-sectional view of the rotor of FIG. 2A;

FIG. 2E is an enlarged view of a portion of a cage of the rotor of FIG.2A;

FIG. 3 is a schematic view of an embodiment of a system in accordancewith the present disclosure; and

FIG. 4 is a schematic view of an embodiment of a chiller system inaccordance with the present disclosure;

FIG. 5 is a cutaway, perspective view of a rotor having a harmonicshunting shield in accordance with another embodiment of the presentdisclosure;

FIG. 6 is a cutaway, perspective view of a rotor having a cageconstruction in accordance with another embodiment of the presentdisclosure;

FIG. 7A is a cutaway, perspective view of another embodiment of a rotorin accordance with the present disclosure;

FIG. 7B is a perspective view showing a magnet of the rotor of FIG. 7A;

FIG. 7C is a perspective view showing a spacer of the rotor of FIG. 7A;and

FIG. 7D is a cross-sectional view of the rotor of FIG. 7A.

The various aspects of the present disclosure mentioned above aredescribed in further detail with reference to the aforementioned figuresand the following detailed description of exemplary embodiments.

DETAILED DESCRIPTION

Particular illustrative embodiments of the present disclosure aredescribed hereinbelow with reference to the accompanying drawings,however, the disclosed embodiments are merely examples of thedisclosure, which may be embodied in various forms. Well-known functionsor constructions and repetitive matter are not described in detail toavoid obscuring the present disclosure in unnecessary or redundantdetail. Therefore, specific structural and functional details disclosedherein are not to be interpreted as limiting, but merely as a basis forthe claims and as a representative basis for teaching one skilled in theart to variously employ the present disclosure in virtually anyappropriately detailed structure. In this description, as well as in thedrawings, like-referenced numbers represent elements which may performthe same, similar, or equivalent functions. The word “exemplary” is usedherein to mean “serving as an example, instance, or illustration.” Anyembodiment described herein as “exemplary” is not necessarily to beconstrued as preferred or advantageous over other embodiments. The word“example” may be used interchangeably with the term “exemplary.”

Certain portions of this disclosure may describe methods having variousportions or steps. It should be appreciated that such portions and/orsteps may be realized by any suitable hardware and/or softwarecomponents configured to perform the specified functions. For example,the present disclosure may employ various integrated circuit components,e.g., memory elements, processing elements, logic elements, look-uptables, and the like, which may carry out a variety of functions underthe control of one or more microprocessors or other control devices.

Embodiments as described herein include electric motors that can accountfor harmonics without using complicated and bulky filters by shuntingthe harmonics to a cooling fluid. These electric motors can be utilizedin any suitable system (e.g., a chiller).

Referring to FIG. 1, a hermetic AC electric motor 100 includes harmonicsshunting such that high frequency harmonics can be shunted from the ACelectric motor 100 without the use of one or more filters. While theembodiments described herein are referred to as a “motor,” those havingordinary skill in the art will understand that the embodiments asdescribed herein can also be used as a generator.

The motor 100 can include a stator 101 having a plurality of poles 104and a rotor 103 disposed within the stator 101 that is in selectivemagnetic communication with the stator 101. The stator 101 can beconfigured to receive and/or output 3-phase current.

A fluid gap 105 exists between the rotor 103 and the stator 101. Thefluid gap 105 is configured to receive a cooling fluid and can includeany suitable size. The fluid gap can be the space between the rotoroutside diameter and the inside surface of the stator bore. The insidesurface of the stator bore can be made up of the combination of thestator lamination teeth and slot wedges. In certain embodiments, the gap105 between the rotor outside diameter and a stator lamination tooth canbe about 0.05 inches to about 0.15 inches. Gaps between the rotoroutside diameter and slot wedges can be on the order of about 0.05inches to about 0.3 inches.

The motor 100 is cooled by a cooling fluid (e.g., refrigerant gas orliquid) that is fed radially and/or axially through the stator core andthrough the gap 105. The gap 105 can receive flow from other systemlocations (e.g., an evaporator, economizer, or condenser of a chillersystem 400 as described below). The cooling fluid is directed throughthe motor stator 101 and/or rotor 103, and is returned to the systemlocation (e.g., evaporator, economizer, condenser). The fluid removesJoule losses associated with high frequency currents at a ratesufficient to ensure reliable component operation without need forinductive, capacitive, or other conventional filters between thevariable speed motor controller 303 and the motor 100.

Referring to FIG. 2A, the rotor 103 can include a cage 107 disposed onthe rotor 103 configured to receive high frequency harmonics and shuntthe high frequency harmonics to the cooling fluid. For example, one ormore portions of the cage 107 can be selected for material and/or shapeto receive the high frequency harmonic electromagnetic energy from thestator 101 and dissipate the energy to the cooling fluid.

Referring additionally to FIGS. 2B-2E, the rotor 103 can include surfacepermanent magnets 109. The surface permanent magnets 109 can be disposedin any suitable order with respect to polarity (e.g., a positive side ofthe rotor 103 and a negative side of the rotor 103).

The cage 107 can also include a plurality of aluminum wedges 111. Eachwedge 111 can be disposed between each surface permanent magnet 109. Thealuminum wedges 111 can include any suitable shape to optimizeconversion of high frequency harmonics to thermal energy through Jouleheating, for example. Any other suitable portion of the rotor 103 and orstator 101 can have any suitable shape to facilitate conversion of highfrequency harmonics to thermal energy to be cooled by refrigerant orother suitable cooling liquid in the fluid gap.

One or more pole gap fillers 113 can also be disposed on the rotor 103.The pole gap filler 113 can be any suitable material (e.g., stainlesssteel). While 2-pole systems are described herein, any suitable numberof poles is contemplated herein, e.g. a positive side of the rotor and anegative side of the rotor arranged in magnetic pole pairs about thecircumference of the rotor.

In certain embodiments, the cage 107 can include one or more aluminumspacers disposed around the rotor 103. As shown, in certain embodiments,the one or more aluminum spacers can include a thick spacer 115 a andtwo thin spacers 115 b disposed axially away from the thick spacer 115 aon opposite sides of the thick spacer 115 a. Any other suitableconfiguration, position, and/or size for the spacers is contemplatedherein.

In certain embodiments, the rotor 103 can further include a sleeve 117disposed around the rotor 103 and the cage 107. The sleeve 117 may bethe same length as the cage 107, or any other suitable size. Inembodiments, sleeve 117 may be formed from carbon fiber compositematerial. In embodiments, sleeve 117 may be formed from inconel.

Referring to FIG. 3, a system 300 includes an AC electric source 301that outputs high frequency harmonics. The system 300 also includes ahermetic AC electric motor 100 as described above connected to the ACelectric source 301 without one or more filters. As shown, the ACelectric motor 100 can be connected to the AC power source 301 through amotor controller 303 (e.g., which controls 3-phase power output to thestator 101).

Motor 100 and/or system 300 can be utilized in any suitable system. Forexample, the motor 100 and/or system 300 can be included in a chillersystem and/or other suitable compressor system for climate control. Anembodiment of a chiller system is shown in FIG. 4.

The motor 100 (or any other suitable motor design) is shown attached tothe compressor to turn the compressor which compresses a refrigerant inthe refrigerant loop 401. The chiller system 400 includes a condenser,an evaporator, and an expansion valve as appreciated by those havingordinary skill in the art.

The condenser can thermally communicate with water from a cooling towerwhich condenses the refrigerant in the refrigerant loop 401. Theevaporator is in fluid thermal communication with water in another waterloop 402 to cool the water. The water circulates to cool a structure asappreciated by those having ordinary skill in the art (e.g., through oneor more air handling units), for example.

As shown in FIG. 4, the refrigerant loop 401 can include a motor branch403 that circulates refrigerant to the motor 100 through the fluid gap105 to remove heat generated by the high frequency harmonics. As shown,in certain embodiments, the motor branch 403 can have its inlet locateddownstream of the expansion valve to receive cooled refrigerant. Theoutlet after passing through the motor 100 can be located downstream ofthe evaporator, in certain embodiments. It is contemplated that anyother suitable location for the inlet and outlet of the motor branch 403can be utilized as will be appreciated by the skilled artisan. Also, itis contemplated that any other suitable cooling fluid and/or circuit(e.g., water in water loop 402, water from the cooling tower) can berouted through the motor 100 in addition to (via a fluidly isolatedcircuit) or alternative of the refrigerant in refrigerant loop 401).

In accordance with at least one aspect of this disclosure, a methodincludes shunting high frequency harmonics to a fluid passing through ahermetic AC electric motor 100. The method can include providing ACelectrical energy from an AC electric source 301 to the AC electricmotor 100 without passing the AC electric energy through a filter.

Shunting can include thermally shunting the high frequency harmonics byconverting the high frequency harmonics to thermal energy in a structurethat is configured to be in thermal communication with the fluid (e.g.,a refrigerant of a chiller) passing through the AC electric motor 100.The structure that is configured to be in thermal communication with thefluid passing through can be a cage 107 on a rotor of the AC electricmotor 100, for example.

High frequency currents are associated with harmonics of the driveswitching frequencies. Drive switching frequencies are typically 10times the motor electrical frequencies (corresponding to, for example,the number of poles × motor RPM/120). These switching frequencies residein the stator but induce current on the rotor. With surface permanentmagnet rotors, eddy currents are induced on the permanent magnetsurfaces. In permanent magnet construction with aluminum bars asdescribed above, the high frequency currents in the stator inducecurrents in the aluminum. Joule heating is the principle by which highfrequency currents are converted into thermal energy, e.g., heating ofthe aluminum. This, in turn, shunts the energy away from the magnets.Removal of the energy from the aluminum bars is accomplished withrefrigerant cooling, as described above, through conductive and/orconvective heat transfer.

Shunting of thermal energy from the magnets may alternatively beachieved through the use of a shield that shunts the high frequencycurrents to the shaft. As shown in FIG. 5, a hermetic AC electric motorin accordance with the present disclosure includes a harmonic-shuntingrotor 500 having a steel shaft 501 that includes an eddy current shield502 disposed coaxially therearound. Shield 502 can be formed from anysuitable material such as aluminum or copper to receive the highfrequency harmonic electromagnetic energy from rotor magnets 503 thoughjoule heating as described above and dissipate thermal energy to shaft501. Preferably, eddy shield 502 is deposited onto shaft 501 using athermal spray technique in which molten coating material, such as copperor aluminum, is atomized and sprayed onto a substrate, e.g., shaft 501.Suitable thermal spray techniques include, without limitation, electricarc spray (twin wire electric arc), flame spray (oxy-acetylene), plasmaspray (APS), and high velocity oxy-fuel (HVOF). In an alternativeembodiment, eddy shield 502 may be deposited onto shaft 501 usingelectroplating. In yet another embodiment, eddy shield 502 may be formedfrom wire that is wrapped onto shaft 501. Rotor 500 may include one ormore non-magnetic spacers 504 disposed between any two or more magnets503.

Shaft 502 is configured to be in thermal communication with a coolingfluid to dissipate heat into the cooling fluid. Shaft 502 mayadditionally or alternatively be configured to dissipate heat into theambient environment. Rotor 500 includes an outer sleeve 505 to protectthe assembly and to mechanically secure aforementioned components ofrotor 500 in place. In some embodiments, sleeve 505 is formed fromcarbon fiber. In some embodiments, sleeve 505 is formed from inconel.Thus, rotor 500 includes, from outside to inside, outer sleeve 505,magnets 503 and/or spacers 504, eddy shield 502, and shaft 501.

FIG. 6 illustrates another embodiment of a harmonic-shunting rotor 550of a hermetic AC electric motor in accordance with the presentdisclosure. Rotor 550 includes a cage 556 disposed around shaft 551.Cage 556 includes a plurality of supports 554 and pockets 557 that aredimensioned to retain magnets 553 to rotor 550. Cage 556 is preferablyformed from aluminum to decrease rotational mass and manufacturing cost,however any suitable material, including copper, may be used.

Rotor 550 may be manufactured by machining pockets 557 into an aluminumtube to form cage 556, pressing cage 556 onto shaft 551, and installingmagnets 553 into pockets 557. In another embodiment, cage 556 may bemanufactured from cylindrical stock by first machining a boretherethrough and proceeding as described above. Magnets 553 are securedin pockets 557 using adhesive and/or press fit. Outer sleeve 555 isfixed to rotor 550 to further secure magnets 553 in place and to providea protective barrier. Outer sleeve 555 may be formed from any suitablematerial as described herein, such as, without limitation, carbon fiberresin, inconel, and the like.

In another method of manufacture, rotor 550 is formed by casting analuminum sleeve onto steel shaft 551, machining pockets 557 into thealuminum sleeve to form cage 556, and installing magnets 553 intopockets 507.

In an embodiment illustrated in FIGS. 7A-D, a hermetic AC electric motorin accordance with the present disclosure includes a harmonic-shuntingrotor 600 having a shaft 601 on which there is defined thereon aplurality of longitudinal facets 608. Eddy shield 602 is deposited ontothe plurality of longitudinal facets 608 to thermally shunt highfrequency harmonics from magnets 603 to shaft 601 as described above.Each facet 608 provides a flat mounting surface onto which a rotormember, such as a magnet 603 or a spacer 604, is affixed. As seen inFIG. 7B, magnet 603 has a nominal bread loaf shape that includes a flatbase surface 609 dimensioned to mate with a corresponding facet 608 ofshaft 601, two angled side surfaces 612, and a curved top surface 610.As best illustrated in FIG. 7D, magnets 603 can be arranged around shaft601 in alternating polarity groups, e.g., two groups of three magnets603 a having a positive polarity field and two groups of three magnets603 b having a negative polarity field. In the exemplary embodimentshown, magnet 603 is a permanent magnet. In embodiments, magnet 603 maybe formed from neodymium and/or samarium cobalt.

One or more magnets 603 may be separated by a spacer 604 that issimilarly-shaped to magnet 603 yet formed from a non-magnetic material,such as, without limitation, aluminum or stainless steel. In someembodiments, spacer 604 may be formed from unmagnetized (inert) magneticmaterial, such as unmagnetized neodymium or unmagnetized samariumcobalt. In the present embodiment, each polarity group is separated by aspacer 604. Spacer 604 has a nominal bread loaf shape that includes aflat base surface 619 dimensioned to mate with a corresponding facet 608of shaft 601, two angled side surfaces 622, and a curved top surface620.

Collectively, the curved top surfaces of magnets 603 and/or spacers 604define an outer circumference of rotor 600 onto which outer sleeve 605is fixed. The side surfaces of magnet 603 and spacers 604 are angled toabut the side surfaces of an adjacent magnet 603 or spacer 604 on eitherside. The disclosed combination of radially-abutting, flat-based magnets603 and/or spacers 604 fixed to faceted mounting surfaces 608 andenclosed within outer sleeve 605 forms an extremely rigid and stablerotor assembly that provides maximum torque transmission from magnets603 to shaft 601. Advantageously, because magnet 603 requires only asingle curved top surface, in contrast to designs with require both topand bottom magnet surfaces to be curved, magnet 603 is simpler tofabricate and thus manufacturing costs may be decreased. Ease ofmanufacture may improve due to the inherent self-aligning nature of thefaceted design. Thermal transfer from magnets 603 to shaft 601 may alsobe improved due to the increased surface area of the disclosed facetedmagnet-shaft interface as compared to a cylindrical magnet-shaftinterface. It is to be understood that, while the exemplary embodimentdepicted in FIGS. 7A-D includes sixteen facets 608 supporting twelvemagnets 603 and four spacers 604, the present disclosure is not solimited. Embodiments of the present disclosure may include a number offacets other than sixteen, and may include a different number of magnetsand/or spacers than illustrated, which can be arranged in anycombination.

As described above, embodiments include a chiller that incorporates,e.g., compressors (e.g., centrifugal, screw, or scroll compressors) witheither induction or permanent magnet motors. The motors can includesurface permanent magnet rotors with aluminum cages surrounding themagnets, stators with axial coolant channels and/or radially fed gascooled air. As described above, embodiments include the application ofhigh speed motor topologies along with variable speed drives oncentrifugal chillers or other suitable systems without the need forexpensive filters between the motor 100 and the variable speed motorcontroller 303.

Particular embodiments of the present disclosure have been describedherein, however, it is to be understood that the disclosed embodimentsare merely examples of the disclosure, which may be embodied in variousforms. Well-known functions or constructions are not described in detailto avoid obscuring the present disclosure in unnecessary detail.Therefore, specific structural and functional details disclosed hereinare not to be interpreted as limiting, but merely as a basis for theclaims and as a representative basis for teaching one skilled in the artto variously employ the present disclosure in any appropriately detailedstructure.

What is claimed is:
 1. A hermetic AC electric motor for a chiller compressor comprising harmonics shunting such that high frequency harmonics can be shunted from the AC electric motor without the use of one or more filters, wherein the hermetic AC electric motor comprises: a stator; and a rotor disposed within the stator and in selective magnetic communication with the stator, wherein a fluid gap exists between the rotor and the stator, wherein the fluid gap is configured to receive a cooling fluid, comprising: a shaft; a plurality of magnets coupled to the rotor; and an eddy current shield, situated between the shaft and the plurality of magnets, that is configured to shunt the high frequency harmonics to the shaft, and to the cooling fluid.
 2. The motor in accordance with claim 1, wherein the eddy current shield is configured as a cage disposed on the rotor.
 3. The motor in accordance with claim 2, wherein the cooling fluid is a refrigerant.
 4. The motor in accordance with claim 2, wherein the rotor includes surface permanent magnets and the cage includes a plurality of aluminum wedges, each wedge disposed between each surface permanent magnet.
 5. The motor in accordance with claim 4, wherein the cage includes one or more aluminum spacers disposed around the rotor.
 6. The motor in accordance with claim 2, further comprising a carbon fiber sleeve disposed around the rotor and the cage.
 7. The motor in accordance with claim 1, further comprising a sleeve disposed around the rotor, situated between the magnets and the stator.
 8. The motor in accordance with claim 7, wherein the sleeve is formed from carbon fiber.
 9. The motor in accordance with claim 1, wherein the eddy current shield is formed from copper.
 10. The motor in accordance with claim 1, wherein the eddy current shield is formed from aluminum.
 11. A simplified variable speed drive system, comprising: an AC electric source that outputs high frequency harmonics; and an AC electric motor for a chiller connected to the AC electric source without one or more filters, wherein the AC electric motor includes harmonics shunting such that the high frequency harmonics are shunted from the AC electric motor without the use of one or more filters, the AC electric motor comprising: a stator coupled to a conduit that receives a cooling fluid from an external device; a shaft; a rotor disposed around the shaft and within the stator and in selective magnetic communication with the stator, wherein a fluid gap exists between the rotor and the stator, and wherein the fluid gap is configured to receive the cooling fluid; and an eddy current shield disposed around the shaft and configured to shunt the high frequency harmonics to the shaft, and to the cooling fluid.
 12. The simplified variable speed drive system in accordance with claim 11, wherein the eddy current shield is configured as a cage disposed on the rotor.
 13. The simplified variable speed drive system in accordance with claim 12, wherein the plurality of magnets are surface permanent magnets and the cage includes a plurality of aluminum wedges, each wedge disposed between each surface permanent magnet.
 14. The simplified variable speed drive system in accordance with claim 13, wherein the cage includes one or more aluminum spacers disposed around the rotor.
 15. The simplified variable speed drive system in accordance with claim 12, further comprising a carbon fiber sleeve disposed around the rotor and the cage.
 16. The simplified variable speed drive system in accordance with claim 11, further comprising a chiller compressor connected to the AC electric motor.
 17. The simplified variable speed drive system in accordance with claim 16, wherein the fluid gap of the AC electric motor is in fluid communication with a refrigerant of the chiller to cool the AC electric motor to thermally shunt the high frequency harmonics.
 18. A simplified variable speed drive system, in accordance with claim 11, further comprising a plurality of magnets disposed around the eddy current shield, such that the eddy current shield is situated between the plurality of magnets and the shaft.
 19. The simplified variable speed drive system in accordance with claim 18, further comprising a sleeve disposed around the rotor.
 20. The simplified variable speed drive system in accordance with claim 19, wherein the sleeve is formed from carbon fiber.
 21. The simplified variable speed drive system in accordance with claim 18, wherein the eddy current shield is formed from copper.
 22. The simplified variable speed drive system in accordance with claim 18, further comprising a chiller compressor connected to the AC electric motor, wherein the shaft of the AC electric motor is in fluid communication with a refrigerant of the chiller to cool the AC electric motor to thermally shunt the high frequency harmonics.
 23. A method, comprising: receiving a cooling fluid that flows through a shaft of a rotor of a hermetic AC electric motor, wherein the cooling fluid is received from an external device; shunting, via an eddy current shield having portions disposed between permanent magnets of the rotor and the shaft, high frequency harmonics to the cooling fluid passing through the shaft of the hermetic AC electric motor.
 24. The method in accordance with claim 23, further comprising providing AC electrical energy from an AC electric source directly to the AC electric motor without passing the AC electric energy through a filter, wherein the AC electric energy includes the high frequency harmonics.
 25. The method in accordance with claim 23, wherein shunting includes converting the high frequency harmonics to thermal energy in the eddy current shield that is configured to be in thermal communication with the cooling fluid passing through the AC electric motor.
 26. A hermetic AC electric motor system not including a filter for removing high frequency harmonics, comprising: a stator; a shaft; a rotor, coupled to the shaft, the rotor comprising permanent magnets, wherein a fluid gap exists between the rotor and the stator, wherein the fluid gap is configured to receive a cooling fluid; and an eddy current shield disposed between the permanent magnets and the shaft and configured to shunt the high frequency harmonics to the shaft and to the cooling fluid. 